Finally, a Likely Explanation for the “Sonic Weapon” Used at the U.S. Embassy in Cuba

How an Ultrasonic Sensor Nearly Derailed a Ph.D. Thesis

Photo: Kevin Fu

Connor Bolton, a Ph.D. student at the University of Michigan, in Ann Arbor, had arranged his workstation just so. He’d painstakingly set up microphones, speakers, and other equipment to test whether sound waves can trigger malfunctions in hard disk drives. When you’re experimenting with precisely calibrated acoustic waves, it’s essential that extraneous signals don’t distort your data.

What he didn’t consider, though, were sounds he couldn’t hear.

One day last August, Bolton [left] and his advisor, Kevin Fu, were discussing the fact that electronic devices can respond in unusual ways to sounds in the environment. Fu mentioned a colleague at the University of Massachusetts, Amherst, whose hearing aid would pick up signals coming from a room-occupancy sensor and then translate the high-frequency chirps into an audible buzz. [To read about Fu’s investigation of another case of electronics behaving badly, see “Finally, a Likely Explanation for the ‘Sonic Weapon’ Used at the U.S. Embassy in Cuba.”]

“Look up, Connor,” Fu told Bolton, pointing to a small white box on the ceiling right above Bolton’s workstation. Such ultrasonic sensors, used to control lighting, emit sound waves inaudible to humans. A change in the reflected sound indicates someone is in the room, and so the lights stay on.

A beat later, just before the picture above was taken, the two realized the sensor might be messing with Bolton’s experiment. The offending sensor was taken down. Fortunately, its signal proved too weak to upend his results.

“There’s always some interference,” Fu notes. “When it’s low intensity, we aren’t concerned. But when we see it in the data, that upsets us.”